Lecithin is a generic name for a mixture mainly comprising various phospholipids, and the major components thereof are phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine (PS), phosphatidylglycerol (PG), phosphatidic acid (PA), and acyl glycero phospholipids including lysophospholipids derived from these phospholipids by hydrolysis of a fatty acid at the sn-1 or the sn-2 position. Lecithin is broadly present in living organisms such as animals, plants, and microorganisms, and is particularly contained much in brains and livers of animals, egg yolks, soybeans, yeasts, and the like. Lecithin is broadly used as a natural emulsifier for foods, industrial products, cosmetics, medicines, and the like. Since lecithin is excellent in preventive effect on oil splattering caused by other ingredients and mold release effect, known examples of edible oils and fats for which lecithin is used include a stir-frying oil, a mold release oil, a fried rice oil, a frying oil, and the like, which are edible oils and fats prepared by addition and dissolution of lecithin. However, when lecithin-containing oil or fat is heated (at a temperature of 120° C. or more), the oil or fat gradually turns brownish yellow, brown, and almost black in the end. Accordingly, when a lecithin-containing oil or fat is used for a stir-frying oil for example, discoloration by heating occurs, leading to problems such as bad appearance of stir-fried dishes.
As a method for suppressing the heat discoloration of lecithin, a method in which an additive for suppressing the discoloration is used has been developed. For example, Patent Literature 1 discloses a method for suppressing the heat discoloration of a lecithin-containing oil or fat, in which polyglycerin-condensed ricinoleic acid ester is added thereto. Moreover, a method in which lecithin is modified has been also developed as a method for suppressing the heat discoloration of lecithin. The causative substances of the heat discoloration of lecithin are phosphatidylethanolamine or α-galacto-oligosaccharides such as raffinose and stachyose, which are involved in the amino-carbonyl reaction considered to be a major cause of heat discoloration. Based on the fact, Patent Literature 2, for example, discloses a lecithin having resistance to heat discoloration obtained by adding a small amount of activated clay or an adsorbent such as silica gel to an alcohol solution of a lecithin, followed by mixing with stirring, removing the adsorbent by filtration, and distilling off the solvent; and a lecithin having resistance to heat discoloration obtained by passing a hydroalcoholic solution of lecithin through a non-polar styrene-vinylbenzene based synthetic resin adsorbent to wash α-galacto-oligosaccharides with hydrous alcohol, eluting lecithin with absolute alcohol, and distilling off the solvent.